The present invention generally relates to superconducting devices. More specifically, the present invention relates to four-port circulators with frequency conversion based on nondegenerate three-wave mixing Josephson devices.
A circulator is a passive nonreciprocal three-port or four-port device, in which a microwave or radio frequency signal entering any port is transmitted to the next port in rotation (only). A port in this context is a plane where an external waveguide or transmission line (such as a microstrip line or a coaxial cable) connects to the device. For a three-port circulator, a signal applied to port 1 only comes out of port 2. A signal applied to port 2 only comes out of port 3. A signal applied to port 3 only comes out of port 1. Within a phase-factor, the scattering matrix for an ideal frequency-preserving three-port circulator is
  S  =            (                                    0                                0                                1                                                1                                0                                0                                                0                                1                                0                              )        .  Circulators are used in superconducting circuits.